Metal Gate Scheme for Device and Methods of Forming

ABSTRACT

Gate structures and methods of forming the gate structures are described. In some embodiments, a method includes forming source/drain regions in a substrate, and forming a gate structure between the source/drain regions. The gate structure includes a gate dielectric layer over the substrate, a work function tuning layer over the gate dielectric layer, a metal-containing compound over the work function tuning layer, and a metal over the metal-containing compound, wherein the metal-containing compound comprises the metal as an element of the compound.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.14/871,580, filed on Sep. 30, 2015, and entitled “Metal Gate Scheme forDevice and Methods of Forming,” which application is hereby incorporatedherein by reference.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment, as examples. Semiconductor devices are typicallyfabricated by sequentially depositing insulating or dielectric layers,conductive layers, and semiconductive layers of material over asemiconductor substrate, and patterning the various material layersusing lithography to form circuit components and elements thereon.

Transistors are circuit components or elements that are often formed onsemiconductor devices. Many transistors may be formed on a semiconductordevice in addition to capacitors, inductors, resistors, diodes,conductive lines, or other elements, depending on the circuit design. Afield effect transistor (FET) is one type of transistor.

Generally in conventional structures, a transistor includes a gate stackformed between source and drain regions. The source and drain regionsmay include a doped region of a substrate and may exhibit a dopingprofile suitable for a particular application. The gate stack ispositioned over the channel region and may include a gate dielectricinterposed between a gate electrode and the channel region in thesubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1 through 8 are cross-sectional views of intermediate stages inthe manufacturing of a Field-Effect Transistor (FET) in accordance withsome embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Field-Effect Transistors (FETs) and methods of forming the same areprovided in accordance with various embodiments. Intermediate stages offorming FETs are illustrated. Some embodiments discussed herein arediscussed in the context of planar FETs formed using a gate-lastprocess. Some embodiments contemplate aspects used in other devices,such as finFETs. Some embodiments are discussed in the context of p-typedevices. Some embodiments are suitable for n-type devices as well. Somevariations of the embodiments are discussed. One of ordinary skill inthe art will readily understand other modifications that may be madethat are contemplated within the scope of other embodiments. Althoughmethod embodiments are discussed in a particular order, various othermethod embodiments may be performed in any logical order and may includefewer or more steps described herein.

FIGS. 1 through 8 are cross-sectional views of intermediate stages inthe manufacturing of a FET in accordance with an exemplary embodiment.FIG. 1 illustrates a substrate 40. The substrate 40 may be asemiconductor substrate, such as a bulk semiconductor substrate, asemiconductor-on-insulator (SOI) substrate, a multi-layered or gradientsubstrate, or the like. The substrate 40 may include a semiconductormaterial, such as an elemental semiconductor including Si and Ge; acompound or alloy semiconductor including SiC, SiGe, GaAs, GaP, GaAsP,AlInAs, AlGaAs, GaInAs, InAs, GaInP, InP, InSb, and/or GaInAsP; or acombination thereof. The substrate 40 may be doped or un-doped. In aspecific example, the substrate 40 is a bulk silicon substrate.

FIG. 2 illustrates the formation of isolation regions 42, such asShallow Trench Isolation (STI) regions, in the substrate 40. In someembodiments, to form the isolation regions 42, trenches are formed inthe substrate 40 by etching. The etching may be any acceptable etchprocess, such as a reactive ion etch (RIE), neutral beam etch (NBE), thelike, or a combination thereof. The etching may be anisotropic. Aninsulation material is formed in the trenches. The insulation materialmay be an oxide, such as silicon oxide, a nitride, the like, or acombination thereof, and may be formed by a high density plasma chemicalvapor deposition (HDP-CVD), a flowable CVD (FCVD) (e.g., a CVD-basedmaterial deposition in a remote plasma system and post curing to make itconvert to another material, such as an oxide), the like, or acombination thereof. Other insulation materials formed by any acceptableprocess may be used. In the illustrated embodiment, the insulationmaterial is silicon oxide formed by a FCVD process. An anneal processmay be performed once the insulation material is formed. Further in FIG.2, a planarization process, such as a chemical mechanical polish (CMP),may remove any excess insulation material and form top surfaces of theisolation regions 42 and a top surface of the substrate 40 that areco-planar.

Although not specifically illustrated, appropriate wells may be formedin the substrate 40. For example, an n-well may be formed in substrate40 where a p-type device, such as a p-type FET, is to be formed. Forexample, to form an n-well in substrate 40, a photoresist can formedover substrate 40. The photoresist can be patterned to expose the regionof the substrate 40 in which the n-well is being formed. The photoresistcan be formed by using a spin-on technique and can be patterned usingacceptable photolithography techniques. Once the photoresist ispatterned, an n-type impurity implant can be performed, and thephotoresist may act as a mask to substantially prevent n-type impuritiesfrom being implanted into the substrate 40 outside of the desiredimplantation area. The n-type impurities may be phosphorus, arsenic, orthe like implanted in the substrate 40 to a concentration of equal to orless than 10¹⁸ cm⁻³, such as between about 10¹⁷ cm⁻³ and about 10¹⁸cm⁻³. After the implant, the photoresist can be removed, such as by anacceptable ashing process. After the implants, an anneal may beperformed to activate impurities that were implanted. The implantationsmay form an n-well in the substrate 40.

Other embodiments are possible. For example, in the manufacturing of ann-type device, p-type impurities may be implanted into substrate 40,instead of n-type impurities, using the same or similar processes tothose described above. The p-type impurities may be boron, BF₂, or thelike, and may be implanted to a concentration of equal to or less than10¹⁸ cm⁻³, such as between about 10¹⁷ cm⁻³ and about 10¹⁸ cm⁻³.

In FIG. 3, a dummy dielectric layer is formed on the substrate 40. Thedummy dielectric layer may be, for example, silicon oxide, siliconnitride, a combination thereof, or the like, and may be deposited orthermally grown according to acceptable techniques, such as CVD, thermaloxidation, or the like. A dummy gate layer is formed over the dummydielectric layer. The dummy gate layer may be deposited, such as byusing CVD or the like, over the dummy dielectric layer and thenplanarized, such as by a CMP. The dummy gate layer may comprise, forexample, polysilicon, although other materials that have a high etchingselectivity may also be used. A mask layer is then formed over the dummygate layer. The mask layer may be deposited, such as by using CVD or thelike, over the dummy gate layer. The mask layer may comprise, forexample, silicon nitride, silicon oxynitride, silicon carbon nitride, orthe like.

The mask layer may be patterned using acceptable photolithography andetching techniques to form mask 50. The pattern of the mask 50 then maybe transferred to the dummy gate layer and dummy dielectric layer by anacceptable etching technique to form dummy gates 48 and dummy gatedielectrics 46 from the dummy gate layer and the dummy dielectric layer,respectively. The etching may comprise an acceptable anisotropicetching, such as RIE, NBE, or the like. A width W of the dummy gate 48and dummy gate dielectric 46 can be in range from about 10 nm to about300 nm, such as about 20 nm. Dummy gate 48 and dummy gate dielectric 46has a combined height H. The height H can be in range from about 50 nmto about 200 nm, such as about 100 nm. An aspect ratio of the height Hto width W can be in a range from about 1 to about 10, such as about 5.The dummy gate 48 covers a channel region in the substrate 40.

Implants for lightly doped source/drain (LDD) regions may be performed.Similar to the implants discussed above, a mask, such as a photoresist,may be formed and patterned over the substrate 40, and p-type impuritiesmay be implanted into the exposed substrate 40 in the LDD regions of ap-type device. The mask may then be removed. The p-type impurities maybe boron, BF₂, or the like. The lightly doped source/drain regions 52may have a concentration of impurities from about 10¹⁵ cm⁻³ to about10¹⁶ cm⁻³. An anneal may be used to activate the implanted impurities.

Other embodiments are possible. For example, in the manufacturing of ann-type device, n-type impurities may be implanted into substrate 40 inthe LDD regions of an n-type device, instead of p-type impurities, usingthe same or similar processes to those described above. The n-typeimpurities may be any of the n-type impurities previously discussed orthe like, and may be implanted to a concentration of equal to or lessthan 10¹⁸ cm⁻³, such as between about 10¹⁷ cm⁻³ and about 10¹⁸ cm⁻³.

Gate spacers 54 are formed along sidewalls of the dummy gate 48 anddummy gate dielectric 46. The gate spacers 54 may be formed byconformally depositing, such as by CVD or the like, a material andsubsequently anisotropically etching the material. The material of thegate spacers 54 may be silicon nitride, silicon carbon nitride, acombination thereof, or the like.

Referring to FIG. 4, epitaxial source/drain regions 56 are formed in thesubstrate 40. A hardmask layer may be formed overlying substrate 40. Thehardmask layer can be silicon nitride, silicon carbon nitride, siliconoxynitride, silicon carbon oxynitride, the like, or a combinationthereof deposited by CVD or the like. Other materials and methods offorming the hardmask layer may be used. The hardmask layer may bepatterned to expose the regions of the substrate 40 where the device isto be formed using any acceptable photolithography and etching process,such as RIE, NBE, or the like. Once the hardmask layer has beenpatterned, an etch selective to the substrate 40 is performed. The etchcan be any acceptable etch, such as a dry or wet etch, which may beanisotropic or isotropic. The etch recesses source/drain regions insubstrate 40. The epitaxial source/drain regions 56 are then epitaxiallygrown in the recesses. The epitaxial growth may be by usingMetal-Organic Chemical Vapor Deposition (MOCVD), Molecular Beam Epitaxy(MBE), Liquid Phase Epitaxy (LPE), Vapor Phase Epitaxy (VPE), the like,or a combination thereof. The epitaxial source/drain regions 56 maycomprise any acceptable material, such as appropriate for the devicetype, e.g., p-type. For example, the epitaxial source/drain regions 56for a p-type device may comprise SiGe, SiGeB, Ge, GeSn, or the like.Then, the hardmask layer may be removed, for example, using an etchselective to the material of the hardmask layer.

Other embodiments are possible. For example, in the manufacturing of ann-type device, epitaxial source/drain regions may comprise silicon, SiC,SiCP, SiP, or the like, and the epitaxial source/drain regions may beformed using the same or similar processes as those described above.

The epitaxial source/drain regions 56 may be implanted with dopants,similar to the process previously discussed for forming lightly dopedsource/drain regions, followed by an anneal. The source/drain regionsmay have an impurity concentration of between about 10¹⁹ cm⁻³ and about10²¹ cm⁻³. The p-type impurities for source/drain regions for a p-typedevice may be any of the p-type impurities previously discussed. In thecase of an n-type device, the n-type impurities may be any of the n-typeimpurities previously discussed. In other embodiments, the epitaxialsource/drain regions 56 may be in situ doped during growth.

In FIG. 4, an etch stop layer (ESL) 58 is conformally formed on theepitaxial source/drain regions 56, gate spacers 54, mask 50, andisolation regions 42. In some embodiments, the ESL 58 may comprisesilicon nitride, silicon carbon nitride, or the like, formed usingAtomic Layer Deposition (ALD), CVD, the like, or a combination thereof.A bottom inter-layer dielectric (ILD0) 60 is deposited over the ESL 58.ILD0 60 may comprise Phospho-Silicate Glass (PSG), Boro-Silicate Glass(BSG), Boron-Doped Phospho-Silicate Glass (BPSG), undoped Silicate Glass(USG), or the like, and may be deposited by any suitable method, such asCVD, plasma-enhanced CVD (PECVD), FCVD, the like, or a combinationthereof.

In FIG. 5, a planarization process, such as a CMP, is performed to levelthe top surface of ILD0 60 with the top surfaces of the dummy gate 48.The CMP may also remove the mask 50 and the ESL 58 from over the dummygate 48. Accordingly, a top surface of the dummy gate 48 is exposedthrough the ILD0 60. The dummy gate 48 and the dummy gate dielectric 46are removed in an etching step(s), so that an opening through the ILD060 and defined by the gate spacers 54 is formed in the substrate 40. Theopening may have an aspect ratio corresponding to the width W and heightH discussed above with respect to FIG. 3 since the opening is defined bythe removal of the dummy gate 48 and dummy gate dielectric 46. Theopening exposes a channel region in a respective active area in thesubstrate 40. The channel region is disposed between a pair of epitaxialsource/drain regions 56. The etching step(s) may be selective to thematerials of the dummy gate 48 and the dummy gate dielectric 46, whichetching may be a dry or wet etching. During the etching, the dummy gatedielectric 46 may be used as an etch stop layer when the dummy gate 48is etched. The dummy gate dielectric 46 may then be etched after theremoval of the dummy gates 48. Although not specifically illustrated,depending on the similarity of materials used for the ILD0 60 and thedummy gate dielectric 46, the ILD0 60 may be recessed when the dummygate dielectric 46 is removed, and this recessing may cause portions ofthe ESL 58 and/or gate spacers 54 to protrude above the top surface ofthe ILD0 60.

An interfacial dielectric 62 is formed in each opening and on thesubstrate 40. The interfacial dielectric 62 may be, for example, anoxide or the like formed by thermal oxidation, chemical oxidation, ALD,or the like. A thickness of the interfacial dielectric 62 may be in arange from about 5 Å to about 15 Å, such as about 8 Å. A gate dielectriclayer 64 is then formed conformally on the top surface of the ILD0 60and in the openings along sidewalls of the gate spacers 54 and on theinterfacial dielectric 62. In some embodiments, the gate dielectriclayer 64 comprises a high-k dielectric material, and in theseembodiments, the gate dielectric layer 64 may have a k value greaterthan about 7.0, and may include a metal oxide or a silicate of Hf, Al,Zr, La, Mg, Ba, Ti, Pb, and combinations thereof. The formation methodsof gate dielectric layer 64 may include ALD, CVD, Molecular-BeamDeposition (MBD), the like, or a combination thereof. A thickness of thegate dielectric layer 64 may be in a range from about 5 Å to about 25 Å,such as about 10 Å.

A capping layer is then formed conformally on the gate dielectric layer64. In the illustrated embodiment, the capping layer comprises a firstsub-layer 66 and a second sub-layer 68. In some embodiments, the cappinglayer may be a single layer or may comprise additional sub-layers. Thecapping layer may function as a barrier layer to prevent a subsequentlydeposited metal-containing material from diffusing into the gatedielectric layer 64. Further, the second sub-layer 68, as illustrated,can function as an etch stop during the formation of a work functiontuning layer if the first sub-layer 66 is formed from a same material asthe work function tuning layer, for example if different layers are tobe formed in different regions, which may include using an etch. Thefirst sub-layer 66 can comprise titanium nitride (TiN) or the likedeposited conformally on the gate dielectric layer 64 by ALD, CVD, orthe like. The second sub-layer 68 can comprise tantalum nitride (TaN) orthe like deposited conformally on the first sub-layer 66 by ALD, CVD, orthe like. A thickness of the capping layer may be in a range from about5 Å to about 20 Å, such as about 10 Å. In the illustrated embodiment, athickness of the first sub-layer 66 may be in a range from about 5 Å toabout 20 Å, such as about 10 Å, and a thickness of the second sub-layer68 may be in a range from about 5 Å to about 20 Å, such as about 10 Å.

A first work function tuning layer 70 is then formed conformally on thecapping layer, e.g., on the second sub-layer 68. The first work functiontuning layer 70 may be any acceptable material with any acceptablethickness to tune a work function of a device, such as a p-type device,to a desired amount given the application of the device to be formed,and may be deposited using any acceptable deposition process. In someembodiments, the first work function tuning layer 70 comprises titaniumnitride (TiN) or the like deposited by ALD, CVD, or the like. Athickness of the first work function tuning layer 70 may be in a rangefrom about 15 Å to about 50 Å, such as about 25 Å.

A layer of a metal-containing material, such as a layer ofmetal-containing compound 78, is then formed conformally on the barrierlayer 76. A metal-containing material, as used herein, is a materialcontaining a metal and a nonmetal (e.g., N, C, O, etc.), where thenon-metal is present in a concentration greater that what may naturallyor incidentally occur by deposition of the metal alone, as one of skillin the art would understand. The metal-containing compound 78 may be atungsten-based compound. For example, the metal-containing compound 78may be WN_(x), WC_(x), WC_(x)N_(y), and/or WC_(x)N_(y)O_(z), or acombination thereof. Other tungsten-based compounds may be used in someembodiments. In some embodiments, a tungsten-based metal-containingcompound layer enables the device to further tune the work function ofthe device to achieve a greater threshold voltage tuning. For example, atungsten-based metal-containing compound layer as described herein mayenable the device to achieve threshold voltages from about 0.1V to about0.4V, such as about 0.2V. In some embodiments, the increased workfunction tuning provided by a tungsten-based metal-containing compoundlayer allows for work function tuning layer 70 to be thinner while stillachieving a desired threshold voltage for the device, which may improvemanufacturing of the device. For example, thinner work function tuninglayers may help to reduce or eliminate problems in filling the gateopening with a subsequent metal layer, which may be difficult where theopening is too narrow because of thicker work function tuning layers. Insome embodiments, the tungsten-based metal-containing compound layer mayhave a smaller resistivity and may reduce the overall gate resistivity,which may be useful in some applications. In some embodiments, thetungsten-based metal-containing compound layer may help to blockdiffusion of certain elements, for example copper and/or fluorine.

In some embodiments, the work function of the metal-containing compound78 may be tuned by changing the composition of the accompanyingnon-metal elements, for example nitrogen, carbon and/or oxygen. Forexample, when metal-containing compound 78 is comprised of WN_(x), thework function of the layer may be tuned by changing the concentration ofN_(x). In the case of WN_(x), the concentration of N_(x) may be variedfrom about 0% to about 50% for work function tuning, and morespecifically from about 15% to about 30%. Other concentrations and othercompounds may be used in some embodiments.

The metal-containing compound 78 may be deposited using any acceptabledeposition process. In some embodiments, the layer of a metal-containingcompound 78 is or the like deposited by physical vapor deposition (PVD),ALD, CVD, or the like. A thickness of the layer of the metal-containingcompound 78 may be in a range from about 10 Å to about 50 Å, such asabout 25 Å.

A metal 82 is formed on the metal-containing compound 78. A workfunction of the metal-containing compound 78 is greater than a workfunction of metal 82. In some embodiments, the metal 82 is comprised oftungsten. The metal 82 may be deposited using any acceptable depositionprocess, such as PVD, CVD, ALD, or the like. The metal 82 fills theunfilled portions of the openings.

In FIG. 7, a planarization process, such as a CMP, may be performed toremove the excess portions of metal-containing compound 78, metal 82,and the layers 64, 66, 68, and 70, which excess portions are over thetop surface of ILD0 60. Then, a controlled etch-back selective to themetal-containing compound 78, metal 82 and the layers 64, 66, 68, and 70is performed to recess those materials, which results in the gatestructures illustrated in FIG. 7, from the top surface of the ILD0 60.The etch-back may comprise an acceptable anisotropic etching, such asRIE, NBE, or the like.

Dielectric cap 86 is formed in the recessed areas formed by theetch-back. To form the dielectric cap 86, a cap dielectric layer can bedeposited in the openings and on the top surface of the ILD0 60. The capdielectric layer may comprise silicon nitride, silicon carbon nitride,or the like, formed using CVD, PECVD, or the like. The cap dielectriclayer can then be planarized, such as by CMP, to form top surfacesco-planar with the top surface of the ILD0 60 thereby forming thedielectric cap.

In FIG. 8, an upper ILD (ILD1) 88 is deposited over the ILD0 60 and thedielectric cap 86, and contacts 90 are formed through the ILD1 88, ILD060, and ESL 58 to the epitaxial source/drain regions 56. ILD1 88 isformed of a dielectric material such as PSG, BSG, BPSG, USG, or thelike, and may be deposited by any suitable method, such as CVD andPECVD. Openings for contacts 90 are formed through the ILD1 88, ILD0 60,and ESL 58. The openings may be formed using acceptable photolithographyand etching techniques. A liner, such as a diffusion barrier layer, anadhesion layer, or the like, and a conductive material are formed in theopenings. The liner may include titanium, titanium nitride, tantalum,tantalum nitride, or the like. The conductive material may be copper, acopper alloy, silver, gold, tungsten, aluminum, nickel, or the like. Aplanarization process, such as a CMP, may be performed to remove excessmaterial from a top surface of the ILD1 88. The remaining liner andconductive material form contacts 90 in the openings. An anneal processmay be performed to form a silicide at the interface between theepitaxial source/drain regions 56 and the contacts 90, respectively.

FIG. 8 illustrates a p-type FET device. The device may have a tunedthreshold voltage due to the metal-containing compound 78, metal 82, andthe layers 64, 66, 68 and 70, included in the gate structure.

Although not explicitly shown, a person having ordinary skill in the artwill readily understand that further processing steps may be performedon the structure in FIG. 8. For example, various Inter-Metal Dielectrics(IMD) and their corresponding metallizations may be formed over ILD1 88.

Some embodiments may achieve advantages. In some embodiments, asdescribed earlier, metal-containing compound 78, which may betungsten-based, may enable the device to further tune the work functionto achieve greater threshold voltage tuning than is possible using onlywork function tuning layer 70. For example, metal-containing compound78, such as a tungsten-based material as described herein, may enablethe device to achieve threshold voltages from about 0.1V to about 0.4V,such as about 0.2V. In some embodiments, the increased work functiontuning provided by a tungsten-based metal-containing compound layerallows for work function tuning layer 70 to be thinner while stillachieving a required threshold voltage, which may improve manufacturingof the device. For example, thinner work function tuning layers may helpto reduce or eliminate problems in filling the gate opening with asubsequent metal layer, which may be difficult where the opening is toonarrow because of thicker work function tuning layers. In someembodiments, the tungsten-based metal-containing compound layer may havea smaller resistivity and may reduce the overall gate resistivity, whichmay be helpful in some applications. In some embodiments, thetungsten-based metal-containing compound layer may help to blockdiffusion of certain elements, for example copper and/or fluorine.

In accordance with some embodiments, a method includes forming a firstsource/drain region and a second source/drain region in a substrate. Agate structure is formed between the first source/drain region and thesecond source/drain region and over the substrate. The gate structureincludes a gate dielectric layer over the substrate, a work functiontuning layer over the gate dielectric layer, a metal-containing compoundover the work function tuning layer, and a metal over themetal-containing compound. The metal-containing compound includes themetal as an element of the compound. The metal-containing compound alsoincludes C, N, O, or a combination thereof.

In accordance with some embodiments, a method includes forming a firstsource/drain region and a second source/drain region in a substrate. Aninter-layer dielectric is formed over the substrate, with an openingthrough the inter-layer dielectric to the substrate between the firstsource/drain region and the second source/drain region. A gatedielectric layer is formed in the opening and over the substrate. A workfunction tuning layer is formed in the opening and over the gatedielectric layer. A metal-containing compound is formed in the openingand over the work function tuning layer. Metal is formed in the openingand over the metal-containing compound. The metal-containing compoundincludes the metal as an element of the metal-containing compound, andthe metal-containing compound has a greater work function that themetal.

In accordance with some embodiments, a structure includes a firstsource/drain region and a second source/drain region in a substrate anda gate structure on the substrate and between the first source/drainregion and the second source/drain region. The gate structure includes agate dielectric layer over the substrate, a work function tuning layerover the gate dielectric layer, a metal-containing compound over thework function tuning layer, and a metal over the metal-containingcompound. The metal-containing compound includes the metal as an elementof the metal-containing compound, and the metal-containing compound hasa greater work function that the metal. The structure includes aninter-layer dielectric over the substrate and around the gate structure.

In accordance with some embodiments, a method includes forming a gatestructure over a substrate. Forming the gate structure includes forminga gate dielectric layer over the substrate. A titanium nitride (TiN)layer is formed over the gate dielectric layer. A tantalum nitride (TaN)layer is formed over the TiN layer. A work function tuning layer isformed over the TaN layer, the work function tuning layer including TiN.A metal-containing compound is formed over the work function tuninglayer, the metal-containing compound including tungsten (W), themetal-containing compound further comprising carbon (C), nitrogen (N),oxygen (0), or a combination thereof. A tungsten layer is formed overthe metal-containing compound. A dielectric cap is formed over topmostsurfaces of the gate dielectric layer, the TiN layer, the TaN layer, thework function tuning layer, the metal-containing compound, and thetungsten layer. A spacer is formed on a sidewall of the gate structure,the spacer extending along and being in physical contact with a sidewallof the dielectric cap.

In accordance with some embodiments, a method includes forming a dummygate structure over a substrate. Spacers are formed on opposingsidewalls of the dummy gate structure. An inter-layer dielectric isformed over the substrate and around the dummy gate structure. The dummygate structure is removed to form an opening through the inter-layerdielectric. A gate dielectric layer is formed in the opening and overthe inter-layer dielectric. A titanium nitride (TiN) layer is formedover the gate dielectric layer. A tantalum nitride (TaN) layer is formedover the TiN layer. A work function tuning layer is formed over the TaNlayer, the work function tuning layer comprising TiN. A metal-containingcompound is formed over the work function tuning layer, themetal-containing compound comprising tungsten (W). A tungsten layer isformed over the metal-containing compound, where the tungsten layeroverfills the opening. The gate dielectric layer, the TiN layer, the TaNlayer, the work function tuning layer, the metal-containing compound,and the tungsten layer below a topmost surface of the inter-layerdielectric are recessed to form a recess in the inter-layer dielectric,the recess exposing sidewalls of the spacers. A dielectric cap is formedin the recess, a topmost surface of the dielectric cap being co-planarwith the topmost surface of the inter-layer dielectric, the dielectriccap being in physical contact with the sidewalls of the spacers.

In accordance with some embodiments, a structure includes a gatestructure on a substrate. The gate structure includes a gate dielectriclayer over the substrate, a titanium nitride (TiN) layer over the gatedielectric layer, a tantalum nitride (TaN) layer over the TiN layer, anda work function tuning layer over the TaN layer, the work functiontuning layer comprising TiN. The gate structure further includes atungsten-containing compound over the work function tuning layer, atungsten layer over the tungsten-containing compound, and a dielectriccap over the tungsten layer, the dielectric cap being in physicalcontact with the gate dielectric layer, the TiN layer, the TaN layer,the work function tuning layer, the tungsten-containing compound, andthe tungsten layer. The structure further includes a spacer on asidewall of the gate structure and a sidewall of the dielectric cap, thespacer being in physical contact with the dielectric cap.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a gate structureover a substrate, wherein forming the gate structure comprises: forminga gate dielectric layer over the substrate; forming a titanium nitride(TiN) layer over the gate dielectric layer; forming a tantalum nitride(TaN) layer over the TiN layer; forming a work function tuning layerover the TaN layer, the work function tuning layer comprising TiN;forming a metal-containing compound over the work function tuning layer,the metal-containing compound comprising tungsten (W), themetal-containing compound further comprising carbon (C), nitrogen (N),oxygen (0), or a combination thereof; forming a tungsten layer over themetal-containing compound; and forming a dielectric cap over topmostsurfaces of the gate dielectric layer, the TiN layer, the TaN layer, thework function tuning layer, the metal-containing compound, and thetungsten layer; and forming a spacer on a sidewall of the gatestructure, the spacer extending along and being in physical contact witha sidewall of the dielectric cap.
 2. The method of claim 1, whereinforming the dielectric cap comprises: recessing the gate dielectriclayer, the TiN layer, the TaN layer, the work function tuning layer, themetal-containing compound, and the tungsten layer to form a recess, therecess exposing a sidewall of the spacer; and filling the recess with adielectric material.
 3. The method of claim 1, further comprisingforming a first epitaxial source/drain structure and a second epitaxialsource/drain structure in the substrate, the gate structure beinginterposed between the first epitaxial source/drain structure and thesecond epitaxial source/drain structure.
 4. The method of claim 1,wherein a work function of the metal-containing compound is greater thana work function of tungsten.
 5. The method of claim 1, furthercomprising tuning a work function of the metal-containing compound bychanging a concentration of nitrogen in the metal-containing compound.6. The method of claim 1, further comprising tuning a work function ofthe metal-containing compound by changing a concentration of oxygen inthe metal-containing compound.
 7. The method of claim 1, wherein themetal-containing compound comprises WC_(x)N_(y)O_(z).
 8. A methodcomprising: forming a dummy gate structure over a substrate; formingspacers on opposing sidewalls of the dummy gate structure; forming aninter-layer dielectric over the substrate and around the dummy gatestructure; removing the dummy gate structure to form an opening throughthe inter-layer dielectric; forming a gate dielectric layer in theopening and over the inter-layer dielectric; forming a titanium nitride(TiN) layer over the gate dielectric layer; forming a tantalum nitride(TaN) layer over the TiN layer; forming a work function tuning layerover the TaN layer, the work function tuning layer comprising TiN;forming a metal-containing compound over the work function tuning layer,the metal-containing compound comprising tungsten (W); forming atungsten layer over the metal-containing compound, wherein the tungstenlayer overfills the opening; recessing the gate dielectric layer, theTiN layer, the TaN layer, the work function tuning layer, themetal-containing compound, and the tungsten layer below a topmostsurface of the inter-layer dielectric to form a recess in theinter-layer dielectric, the recess exposing sidewalls of the spacers;and forming a dielectric cap in the recess, a topmost surface of thedielectric cap being co-planar with the topmost surface of theinter-layer dielectric, the dielectric cap being in physical contactwith the sidewalls of the spacers.
 9. The method of claim 8, furthercomprising forming a first epitaxial source/drain structure and a secondepitaxial source/drain structure in the substrate, the dummy gatestructure being interposed between the first epitaxial source/drainstructure and the second epitaxial source/drain structure.
 10. Themethod of claim 9, further comprising forming an etch stop layer overthe dummy gate structure, the first epitaxial source/drain structure andthe second epitaxial source/drain structure.
 11. The method of claim 8,further comprising, after forming the tungsten layer, removing excessportions of the tungsten layer overfilling the opening.
 12. The methodof claim 8, wherein a work function of the metal-containing compound isgreater than a work function of tungsten.
 13. The method of claim 8,further comprising tuning a work function of the metal-containingcompound by changing a concentration of carbon in the metal-containingcompound.
 14. The method of claim 8, wherein the metal-containingcompound comprises WC_(x)N_(y)O_(z).
 15. A structure comprising: a gatestructure on a substrate, the gate structure comprising: a gatedielectric layer over the substrate; a titanium nitride (TiN) layer overthe gate dielectric layer; a tantalum nitride (TaN) layer over the TiNlayer; a work function tuning layer over the TaN layer, the workfunction tuning layer comprising TiN; a tungsten-containing compoundover the work function tuning layer; a tungsten layer over thetungsten-containing compound; and a dielectric cap over the tungstenlayer, the dielectric cap being in physical contact with the gatedielectric layer, the TiN layer, the TaN layer, the work function tuninglayer, the tungsten-containing compound, and the tungsten layer; and aspacer on a sidewall of the gate structure and a sidewall of thedielectric cap, the spacer being in physical contact with the dielectriccap.
 16. The structure of claim 15, further comprising a first epitaxialsource/drain structure and a second epitaxial source/drain structure inthe substrate, the gate structure being interposed between the firstepitaxial source/drain structure and the second epitaxial source/drainstructure.
 17. The structure of claim 15, wherein a work function of thetungsten-containing compound is greater than a work function oftungsten.
 18. The structure of claim 15, further comprising aninter-layer dielectric around the gate structure, a top surface of theinter-layer dielectric being substantially level with a topmost surfaceof the dielectric cap.
 19. The structure of claim 18, further comprisingan etch stop layer separating the spacer from the inter-layerdielectric.
 20. The structure of claim 15, further comprising aninterfacial dielectric layer interposed between the substrate and thegate dielectric layer.